Non-woven batts possessing excellent tensile strength, tear strength and initial modulus

ABSTRACT

Non-woven batts possessing excellent tensile strength, tear strength and initial modulus are comprised of isotactic polypropylene substrate fibers bonded together by an ethylenepropylene random copolymer, said copolymers advantageously having an ethylene content of between about 3 to 20 mole percent. The ethylene-propylene random copolymer is desirably present in the proportion of approximately 5 to 75 weight percent relative to the weight of the isotactic polypropylene fibers.

United States Patent [191 Kanehira et al.

[ Oct. 21, 1975 NON-WOVEN BATTS POSSESSING EXCELLENT TENSILE STRENGTH,TEAR STRENGTH AND INITIAL MODULUS [75] Inventors: Hiroshi Kanehira,Kurashiki; Syozi Kurosaki, Okayama, both of Japan [73] Assignee: KurarayCo., Ltd., Kurashiki, Japan [22] Filed: Sept. 11, 1973 [21] Appl. No.:396,136

[30] Foreign Application Priority Data Sept. 14, 1972 Japan 47-72427[52] US. Cl. 428/288; 156/181; 156/283 [51] Int. Cl. B32B 5/28; D04B H58[58] Field of Search 161/170, 150, 157, 252;

[56] References Cited UNITED STATES PATENTS 3,049,466 8/1962 Erlich161/150 3,393,685 7/1968 Mumpower 161/170 3,501,369 3/1970 Derlich161/170 3,502,538 3/1970 Petersen 161/170 3,671,383 6/1972 Sakata161/252 FOREIGN PATENTS OR APPLICATIONS 3,511,784 8/1960 Japan 4,226,83012/1967 Japan Primary Examiner-George F. Lesmes Assistant ExaminerEllisP. Robinson Attorney, Agent, or Firm-Bacon & Thomas [5 7 ABSTRACT 4Claims, No Drawings NON-WOVEN BATTS POSSESSING EXCELLENT TENSILESTRENGTH, TEAR STRENGTH AND INITIAL MODULUS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to novelnon-woven batts, e.g.,

non-woven fabrics, comprised of isotac'tic polypropylene substratefibers which are bonded together by an ethylene-propylenerandomcopolymer, said copoly-:

meradvantageously having an ethylene content of approximately 3 to 20mole percent. These novel batts possess excellent tensile strength, tearstrength and initial modulus. The non-woven batts ofrthis inventionexhibit particularly advantageous properties when in the configurationof a spun-bonded, non-woven batt.

2. Description of the Prior-Art Spun-bonded, non-woven batts or fabricshave been developed with superior tensile strength as compared tonon-woven batts of staple fibers. See U.S. Pat. No. 3,338,992 and U.S.Pat. No. 3,341,394yHowever, nonwoven batts irreproachable from apractical viewpoint cannot be obtained according to the methodsdisclosed therein regardless of the polymer selected. The prior artteaches a method of incorporating small amounts of adhesive fiber intothe substrate fibers with subsequent melting of the adhesive fibers toeffect bonding of the substrate fibers. For instance, it is taught thatpolycaproamide (Nylon 6) fibers or a copolymer or mixture ofpolycaproamide and polyhexamethylene adipamide (Nylon 66) can beemployed as-the adhesive fibers for polyhexamethylene adipamidesubstrate fibers, and that fibers comprising a copolymer of ethyleneterephthalateand ethylene isophthalate, or polyethylene terephthalatefibers having a low degree of molecular orientation, can be utilized asthe adhesive fibers for polyethylene terephthalate substrate fibers.

Furthermore, in U.S. Pat. No. 3,322,607 and U.S. Pat. No. 3,276,944, itis disclosed that self-bonded, non-woven fabrics may be prepared fromisotactic polypropylene or copolymers composed mainly of ethylene andpropylene. However, as is clear from the results shown in thecomparative examples, infra, these self-bonded, non-woven batts-do notpossess the excellent mechanical properties which can be obtainedaccording to this invention.

Still further, Japanese Patent Publication No. 11784/60 and JapanesePatent Publication No. 26830/67 disclose that the tenacity of shapedarticles prepared from polypropylene fibers can be improved by formingthereon a coating of an ethylene-propylene copolymer containing anorganic peroxide, a curing agent and the like. The ethylene content ofthe ethylene-propylene copolymer used in this proposal ranges from 20 to80 mole percent, with 55 mole percent the norm.

Although various attempts have-been made to improve the tenacity ofnon-woven, fabrics composed mainly of isotactic polypropylene fibersdescribed hereinabove, bonded non-woven batts, e.g., non-woven fabricsand the like, obtained according to these methods are stillunsatisfactory as illustrated in the following comparative examples.

In addition to the foregoing methods incorporating adhesive fibers withsubstrate fibers, there have also beenemployed for similar .purposemethods of spraying an adhesive rubber latex onto nonwoven batts or im-SUMMARY OF THE INVENTlON Accordingly, it is the primary object of thisinvention to obviate deficiencies in the prior art thereby yielding anon-woven batt of polypropylene fibers bonded together by anethylene-propylene random copolymer, which batt exhibits excellentmechanical properties.

It is another object of the present invention to provide such anon-woven batt wherein polypropylene continuous filaments are employedto yield a spunbonded, non-woven batt.

It has now been found that among the bonding methods detailedhereinabove, the method of incorporating a component capable of melting(hereinafter referred to as the hot melting component and represented bythe ethylene-propylene copolymer) along with the substrate fibers, andmelting that component to bond the substrate fibers, is most desired;and that in the case of isotactic polypropylene substrate fibers,optimum results are obtained when an ethylene-propylene randomcopolymer, especially one having an ethylene content of approximately 3m30 mole percent, is employed as the adhesive component in an amount ofapproximately 5 to 75,weight percent relative to the weight of thesubstrate fibers.

DETAILED DESCRIPTION or THE INVENTION The substrate fibers of thenon-woven batts of this invention are comprised of isotacticpolypropylene. While the lengths of thesubstrate fiber is notparticularly critical, e.g., fiber length, staple fiber length, etc.,-

improve the mechanical properties thereof and it is the most prominentfeature of this invention that a specific adhesive component beutilized. Furthermore, it is indispensible that this hot meltingcomponent be a random copolymer of ethylene and propylene monomers,

if the intended objects of this invention are.to be attained.

If an ethylene-propylene block copolymer were to be.

incorporated as the hot melting component, even if the ethylene contentbe within the range specified by this invention, substantial improvementin mechanical properties would not be realized. The physical propertiesof such a block copolymer resemble those of a blend of polypropylene andpolyethylene and neither polymer is itself suited as the adhesivecomponent.

Not only is it important to this invention that the adhesive be a randomcopolymer, it is also necessary that the ethylene content of the randomcopolymer be lower than the propylene content, i.e., be lower than 50percent, and most preferably be within the range of from 3 to 20 molepercent. Should the ethylene content be lower than 3 mole percent, thebonding operation experiences difficulties due to the smalldifference-between the melting points of the hot melting component andthe substrate fibers. Should the ethylene content exceed 20 molepercent, particularly the 50 mole percent or more illustrated inJapanese Patent Publication No. 1 1784/60, the elastic properties of thebatt reside in the .hot melting component and, therefore, markeddegradation of the initial modulus is observed. The hot meltingcomponent according to the invention is ad vantageously crystalline andhas a melting point at least 10C. lower than the melting point of thesubstrate fibers; the most preferred ethylene content of the hotmeltingcomponent utilized in this invention is about 4 to 6 mole percent.

While the hot melting component may take any one of a number of physicalforms, for instance, fiber, film or powder, it is indispensible that thehot melting component be incorporated into the isotactic polypropylenesubstrate fibers in the approximate proportion of from to 75 weightpercent relative to the weight of the substrate fibers. When the amountof the hot melting component is less than 5 weight percent, no prominentimprovement of mechanical properties, particularly tensile strength, isobserved; should the amount of the hot melting component exceed 75weight percent, the tear strength is drastically reduced. It ispreferred that the hot melting component be incorporated in an amount ofapproximately 7 to 30 weight percent relative to the weight of thesubstrate fibers to yield nonwoven batts of high tenacity, high tearstrength and high initial modulus.

In accordance with the preferred embodiment of this invention, both thehot melting component and the substrate are in fibrous form, mostpreferably in filamentary form. To facilitate the accurate monitoring ofthe proper proportions of each component, bothmay be extruded from thesame spinneret or, alternatively, from adjacent spinnerets. In eithercase, the fibers filaments or yarn thus extruded are accummulated on areceiving surface disposed therebelow. To aid in such depositiontechnique, there can be disposed below the spinneret head either afilament or yarn suction device or a device for generating a charge ofstatic electricity or electrostatic field. It is also within the ambitof this invention to extrude the filaments from a large diameter orificespinneret in combination with the utilization of high pressure fluids.Optionally, the hot melting component may be added in the form of eitherfibers, staple fibers or powder, or the like, to the isotacticpolypropylene substrate fibers and intimately admixed therewith, mostdesirably such forms of the hot melting component are simply added to anexisting non-woven batt comprised of the isotactic polypropylene fiberson the surface of the said batt or at the interior thereof, or both.

Further in attaining the objects of this invention, the hot meltingcomponent is melted by means of any suitable heat treatment and then thebatt is subjected to pressure, desirably concurrently therewith, toeffect the bonding between and among the substrate fibers and thusconsolidate the batt. The heat treatment should be carried out at atemperature between not higher than the melting point of the substratefiber and lower than that of the hot melting component by up to 20C. orless. Preferably, this treatment is conducted at a temperature withinthe range of the melting point of the substrate fiber and higher than10C. lower than the melting point of the hot melt component.Conventional hot pressing techniques, i.e., with hot rolls or hotpresses, may be employed for this purpose. For example, there can beemployed that method comprising inserting the non-woven battsincorporating the hot melting component between hot pressure plates orhot pressure rollers to melt the said hot melting component andsimultaneously consolidate the fabric. By this particular hot presstreatment, the ethylene-propylene random copolymer componentincorporated in the non-woven batt is substantially completely meltedand the substrate fibers are thence bonded to one another, concomitantlyresulting in the disappearance of any fluff from the surface of the saidnon-woven batt. Consequently, there is thus obtained a non-woven batthaving a high tensile strength, a high tear strength and a high initialmodulus.

As will be seen from the examples and comparative examples which follow,the isotactic polypropylene non-woven batts of this invention exhibitmechanical properties much higher than those which can be attained withnon-woven batts of isotactic polypropylene consolidated by means of hotmelt techniques other than those specified according to the invention.Thus, in order to further illustrate the invention and the advantagesthereof, such specific examples are given, it being understood that thesame are intended merely as illustrative and in no wise limitative.

EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 1 TO 9 Isotactic polypropylenehaving a melt index of 30 was extruded at a rate of 80 g/min from aspinneret maintained at 265C. and having 20 orificies, each with adiameter of 1.2 mm. An ethylene-propylene random copolymer having anethylene content of 5 mole percent and a melt index of 5 was extruded ata rate of 16 g/min from a spinneret maintained at 280C. and having 4orifices, each of the same diameter as above. These extruded filaments(yarn) were all stretched by means of corresponding, individual take-uprollers positioned 5 cm below each spinneret. The take-up rate was about3800 m/min in the case of the polypropylene yarn and about 1800 m/min inthe case of the copolymer yarn. Both types of the stretched yarns werenext introduced into an air nozzle disposed below the take-up rollersand subsequently deposited on a moving metal wire net having a suctionmachine at the lower portion thereof. Thence was obtained a soft,flexible non-woven fabric having a weight of g/m The non-woven fabricthus formed was hot-pressed at 158C. for 3 minutes under a pressure of0.5 Kg/cm between metal wire nets of mesh, to thereby melt theethylene-propylene random copolymer filaments present in the non-wovenfabric. It was observed that uniform bonding was attained throughout thesectional direction of the batt with no surface fluffs thereon.Properties of the resultant non-woven fabrics are shown in Table I.

In accordance with the foregoing method, nonwoven fabrics were preparedby employing various hot melting polymers (in each case, the weight ofthe nonwoven fabric was 100 g/m Properties of these nonwoven fabrics arealso shown in Table 1. In comparative Examples 4 and 7, the hot meltingpolymer was employed in powder form.

the non-woven fabrics of isotactic polypropylene filaments (Example 4).The results of these latter experiments are shown in Table 2.

TABLE 2 Melting Polymer to lsotactic Polypropylene TABLE 1 Ex.Hot-Melting Mixing Ratio Melting No Polymer of Hot Melting TreatmentThickness 1 Polymer to of Non-Woven lsotactic Temp. Time Fabrics afterTensile Initial Tear Remarks Polypropylene Melting Treat- StrengthModulus Strength (bonding Flbers (parts) (C) (min.) ment (mm) (Kg/cm)(Kg/mm) (Kg) conditions) Ex. I ethylene-propylene 20 158 3 0.30 8.0 15.26.2 no fluffs on random copolymer th sh r (ethylene content; surface 5mole Ex; 2 ditto (ethylene (cgrgtent; l6 mole i 155 3 0.32 7.5 11.0 8.3ditto D Comparditto (ethylene I ativc content; mole 4 158 3 0.38 29 13.67.1 fluffs on Ex. 1 the sheet surface Comparditto (ethylene 85 l58 30.28 7.0 l6.l 3.0 film-like ative content; 5 mole (excessive Ex. ,2bonding) Comparditto (ethylene I0 I58 3 0.40 2.4 13.0 7.l insufficientative content; 2 mole bonding Ex. 3

. g 165 3 0.25 5.0 l7.4 2.0 film-like,

semi- I transparent Comparditto (ethylene [0 M0 3 0.35 5.2 6.7 8.5 ativecontent; 28 mole Ex. .4 Comparethylene-propylene I60 3 0.40 2.5 l3.6 7lfluffs on ative block copolymer the sheet Ex. 5 (ethylene content;surface 7 mole Comparisotactic poly- 10 160 3 0.40 3.6 13.3 8.0insufficient ative propylene having bonding Ex. 6 low molecularorientation I65 3 0.25 5.0 16.5 2.5 film-like Comparatactic poly- 10 I403 0.40 L8 8.2 6.3 ative propylene Ex. 7 Comparhigh density l0 M5 3 0.414.0 9.6 7.5 ative polyethylene Ex. 8 Compar ethylene-vinyl 10 140 3 0.425.0 7.4 6.1 ative acetate copolymer Ex. 9 (vinyl acetate content; moleAs is apparent from the results shown in Table 1, only TABLE 2 Cont1nuednon-woven fabrics according to this invention have excellent mechanicalproperties in the sense of tensile st r- Example 'P 3 Example 4 ength,tear strength and initial modulus. Differences in Hot Meltingethylene-propylene ethylene-propylene values relative to theseproperties, between the non- Polymer randmn Wimlymer randm Polymer(ethylene content; (ethylene content; woven fabrics obtained in theExamples according to 4 mole 10 mo|e this invention and those obtainedin the Comparative Examples, are markedly probative. azfi i gziTemperature (C) 160 160 EXAMPLES 3 AND 4 Melting Treatment Time (min.) 33 Thickness of 0- The procedures of Examples 1 and 2 were repeatedNon-Woven Fabrics in the same manner, except that the hot melting comm)ponent was not incorporated in the form of filaments Tensile strength7.3 7.4 but was mixed in the form of staple fibers with the nonl l 5 513 0 woven fabrics of isostatic polypropylene filaments (Exz z u ample3) or was sprinkled in the form of powder onto '(Tar; Strength 6.6 6.2

As will be seen from the results shown in Table 2, non-woven fabricshaving properties equivalent to those non-woven fabrics obtained by thespun-bonding method can be obtained by other various methods accordingto the invention.

COMPARATIVE EXAMPLES 10 AND 11 The procedures of Example 1 were repeatedin the same manner, except that in one instance the hot meltingfilaments of the ethylene-propylene random copolymer having an ethylenecontent of 5 mole percent were not incorporated, namely, isotacticpolypropylene filaments alone were employed (Comparative Example 10),and in the second instance the hot melting filaments alone wereemployed, namely, the isotactic polypropylene filaments were not used(Comparative Example l l Mechanical properties of the obtained nonwovenfabrics (each being a self-bonded non-woven fabric) are shown in Table3.

TABLE 3 Example N0. Comparative Comparative Example l Example 11 TensileStrength (Kg/cm) 3.2 2 3 Initial Modulus (Kglmm 16.8 6 Tear Strength(Kg) 5 0 4 9 can be made without departing from the spirit of theinvention. It is intended, therefore, that the invention be limited onlyby the scope of the following claims.

What is claimed is: v

1. A non-woven batt having high tensile strength, high tear strength andhigh initial modulus, which comprises a batt of isotactic polypropylenesubstrate fibers bonded together by means of an ethylene-propylenerandom copolymer wherein the ethylene content of said ethylene-propylenerandom copolymer is from 4 to 6 mole percent and is present in theapproximate proportion of 5 to weight percent relative to the weight ofsaid isotactic polypropylene substrate fibers.

2. A non-woven batt according to claim 1, wherein saidethylene-propylene random copolymer is present in the approximateproportion of 7 to 30 weight percent relative to the weight of saidisotactic polypropylene substrate fibers.

3. A non-woven batt according to claim 1, wherein said isotacticpolypropylene component is in the form of continuous filaments.

4. A non-woven batt according to claim 2, wherein said isotacticpolypropylene component is in the form of continuous filaments.

1. A NON-WOVEN BATT HAVING HIGH TENSILE STRENGTH, HIGH TEAR STRENGTH ANDHIGH INITIAL MODULUS, WHICH COMPRISES A BATT OF ISOTACTIC POLYPROPYLENESUBSTRATE FIBERS BONDED TOGETHER BY MEANS OF AN ETHYLENE-PROPYLENERANDOM COPOLYMER WHEREIN THE ETHYLENE CONTENT OF SAID ETHYLENE-PROPYLENERANDOM COPOLYMER IS FROM 4 TO 6 MOLE PERCENT AND IS PRESENT IN THEAPPROXIMATE PROPORTION OF 5 TO 75 WEIGHT PERCENT RELATIVE TO THE WEIGHTOF SAID ISOTACTIC POLYPROPYLENE SUBSTRATE FIBERS.
 2. A non-woven battaccording to claim 1, wherein said ethylene-propylene random copolymeris present in the approximate proportion of 7 to 30 weight percentrelative to the weight of said isotactic polypropylene substrate fibers.3. A non-woven batt according to claim 1, wherein said isotacticpolypropylene component is in the form of continuous filaments.
 4. Anon-woven batt according to claim 2, wherein said isotacticpolypropylene component is in the form of continuous filaments.